Name the chemical substance which changes pepsinogen into its active form.

Explanation

To answer the question about the chemical substance that converts pepsinogen into its active form, follow these steps:

### Step-by-Step Solution:

1. **Identify Pepsinogen**: Understand that pepsinogen is an inactive enzyme (zymogen) secreted by the gastric glands in the stomach. It is the precursor to the active enzyme pepsin, which is essential for protein digestion.

2. **Determine the Active Form**: Recognize that the active form of pepsinogen is pepsin. Pepsin is responsible for breaking down proteins into smaller peptides.

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